1. Field of the Invention
The present invention relates to a printhead and a recording device arranged with the printhead, and in particular to a printhead for realizing high speed and high image quality and a recording device arranged with the printhead.
2. Description of the Related Art
Conventionally, with respect to printer printheads that use thermal energy or the like to conduct image recording, printheads that form dots by scattering liquid ink as small drops (so-called liquid drops) onto a recording medium to record an image are known. Printers that record an image by forming dots using a printhead such as a thermal head that supplies thermal energy to a heat-sensitive recording medium are also known.
In recent years, a printer arranged with plural printheads has been practically applied with the object of obtaining a multicolor image with a high resolution and at a high speed. In this printer, a multicolor image can be obtained by making the printheads correspond per color and overlapping the color images in order to obtain an image corresponding to the respective colors. In this case, because displacement of elements between the printheads leads to color displacement and to low resolution, positions between the plural printheads, i.e., the positions of dots to be formed by the respective printheads, must be aligned with high precision.
Thus, in a recording device having plural printheads having numerous nozzles that discharge liquid ink drops, in a case where the printheads are plurally arranged in a direction (main scanning direction) orthogonal to the arranging direction (subscanning direction) of the nozzles, technology where positional displacement in regard to the subscanning direction of dots to be formed between the printheads is corrected (referred to below as subscanning registration correction) has been disclosed (e.g., see Patent Document 1: Japanese Patent Application Laid-Open Publication (JP-A) No. 62-077951, pp. 2-3 and FIG. 2). In this technology, the printheads are fixed, and common nozzle groups between a fixed number of printheads that is less than the number of mounted nozzles are used.
However, positional displacement in regard to the main scanning direction of the dots to be formed between the printheads (referred to below as main scanning registration correction) cannot be corrected with this technology by itself.
As another example of subscanning registration correction, technology has also been disclosed where each of plural printheads is mechanically and movably created and each of the printheads is moved, whereby displacement is corrected (e.g., see Patent Document 2: JP-A No. 05-238004, pp. 3-4 and FIG. 2). However, in this technology, because mechanical members for enabling the printheads to be movable are large, the printheads themselves become large. Thus, the application of large printheads, such as paper-width printheads, is difficult.
Incidentally, in a case where plural printheads are driven, it is necessary to effectively drive each printhead. For example, it has become possible to arrange, at a high density, nozzles and heater elements numerously arranged in the subscanning direction. By arranging numerous nozzles and heater elements at a high density, dot formation at a high density has become possible. However, a high-capacity power source is necessary in order to simultaneously drive the numerous nozzles and heater elements lined up in the subscanning direction within the printheads.
Thus, driving in the subscanning direction according to one printhead is conducted by a time division in which the drive number of nozzles and heater elements is fixed to a predetermined number and the nozzles and heater elements of that predetermined number are grouped into single blocks and driven per block. That is, the drive timing per block is slightly staggered so that the nozzles and heater elements are successively driven, whereby it has become possible to control instantaneously flowing current and it has become possible to render high-capacity power sources unnecessary.
However, when numerous nozzles and heater elements are arranged and driven, wiring increases and nozzle trouble increases. For this reason, print element driving technology has been disclosed where a counter is mounted within a semiconductor chip of an inkjet recording head unit, a clock is supplied to the counter, the counting output of the clock is internally generated as a block enable signal and the blocks are selected (e.g., see Patent Document 3: JP-A No. 06-305148, pp. 3-4 and FIG. 1). However, in this technology, because the order of block selection is fixed, the technology is not compatible with main scanning registration correction.
As another example of print element driving, technology has been disclosed where a phase-delay time between nozzles is set in order to raise the drive frequency of the nozzles (e.g., see Patent Document 4: JP-A No. 06-198893, pp. 2-3 and FIG. 3). In this technology, the nozzles are grouped into four nozzle groups every other three and each nozzle group is driven by staggering its phase with the other nozzle groups. However, in this technology, because the number of print elements per group (=number of simultaneously driven print elements) becomes large, application of this technology with respect to printheads where the number of mounted print elements is large is difficult.
Moreover, as another example of print element driving, technology has been disclosed where a decoder is mounted within a drive circuit of a recording head and the blocks are selected by an output signal of the decoder in order to reduce wiring and deter nozzle trouble (e.g., see Patent Document 5: JP-A No. 09-327914, pp. 6-7 and FIG. 7). However, in this technology, because an external signal is required each time the selected block is switched, control becomes complicated.
As described above, in each of the conventional technologies, although subscanning registration correction and print element driving are possible, it has been difficult to realize both main scanning registration correction and subscanning registration correction. That is, in each of the above-described conventional technologies, both main scanning registration correction and subscanning registration correction cannot be achieved.
For example, in a configuration that combines the above-described conventional technologies, even if a decoder is mounted, different control signals are invariably required when switching the selected block. Also, in a case where the printheads are configured so that each of plural printheads is mechanically movable, the mechanism for adjusting each printhead becomes large.
Here, it will be assumed that main scanning registration correction is possible by print element driving and that subscanning registration correction is possible by adjusting the positional relation of the printheads. The reason why main scanning registration correction is difficult in the above-described conventional technologies will be described.
It should be noted that, in order to facilitate understanding of the problems with respect to main scanning registration correction, a case will be described here where, in a recording device having plural printheads having numerous nozzles that discharge liquid ink drops, subscanning registration correction is conducted by recording using common nozzle groups between printheads of a fixed number that is less than the number of mounted nozzles and main scanning registration correction is conducted by mounting a counter within a drive circuit of a recording head and using an output signal of the counter to select the blocks.
Because drive print elements are successively driven per block, a time difference arises in the drive timing of each block. Because the printheads that are relatively main-scanned over the recording medium are in a constantly moving state during the print element driving, dots positions on the recording medium are displaced by the amount of the time difference. The displacement amount of the dot positions increases together with an increase in the main scanning speed. When each block is periodically driven at a fixed time difference, the displacement amount of the dot positions reaches a maximum.
For example, a case will be considered where, as shown in FIG. 36, the printheads are divided into eight blocks, a print element A belonging to an initially selected block plots a dot on line A on a recording medium and a print element B belonging to a finally selected block simultaneously plots a dot on line B. When a print element B of a different printhead plots a dot on line A due to subscanning registration correction, the dot is not plotted at the position represented by the solid circle on line A but is plotted at the position represented by the dotted circle because the selection order of the blocks is fixed (occurrence of main scanning registration displacement). Because the plotting print element changes in accordance with the subscanning registration amount, the displacement amount between the solid circle and the dotted circle on line A changes.